This invention relates to a radial ply pneumatic tire, more specifically to an improved cross section profile for such tires.
Subtle changes in the molded shape of a pneumatic radial tire, the materials used to make the tire, the design of the tread pattern or the belt package or the reinforcing members can improve or detract from the performance of the tire. The tire designer is under constant pressure to improve the overall performance of the tire. In his pursuit of improving the product, he often must reverse or abandon the previously conceived design approaches and start anew with previously considered unworkable designs or approaches which when creatively applied in a new way solve problems or achieve performance goals heretofore believed unachievable.
Pneumatic tires are one of the most complex laminated composite structures devised by man. They are inherently difficult to correctly model and are routinely simplified in analysis leading to clearly erroneous design theories and approaches.
The very nature of the tire makes it possible for many conflicting design approaches to survive and even flourish because the structure is so complex that multiple variables are constantly being adjusted to optimize a particular design theory.
One particularly important variable that influences a tires performance is its molded shape and its resultant cross sectional profile when the tire is mounted and inflated on its design rim.
Rhyne et al in U.S. Pat. No. 5,637,162 assigned to Michelin teaches a tire structure for Improved Tread Life that claims a particular carcass and belt profile when the tire is properly inflated. The profile has a smaller than normal outside diameter combined with a larger cross-sectional width which enables a tread to have a flatter wider tread arc width which reduced the contact pressure across the tread profile. The resultant profile enables the tread life to achieve about 100,000 miles of service. Its tread width as taught extends axially outwardly of the mounted bead width.
An earlier U.S. Pat. No. 4,669,519 issued Jun. 1, 1987 to Tagaski et al, teaches a Reduced Rolling Resistance Pneumatic Radial Tire which has a molded lower sidewall and bead area that is 20%-50% wider than its design rim width. The tires profile is such that the maximum section width is located radially in the upper sidewall region or greater than 50% of the tires section height as measured from the nominal rim diameter. The conventional radial tire has the maximum section width located at a radial height about 50% of the section height. This Bridgestone Patent teaches that the hysterectic shear stresses in the shoulder region of the sidewall generates the most losses in terms of rolling resistance and that by minimizing these losses a benefit in reduced rolling resistance can be achieved because the tread shoulders will run cooler.
Both of these diverging solutions are plausibly correct. That is the beauty of the tire art. The engineers can practice what appears to be contradicting approaches to get to a similar improved result. It is for that reason that so many patents are issued. The unexpected results abound. Those of ordinary skill in the tire art routinely teach away from particular ideas, which are latter, discovered to provide beneficial solutions.
The prior art Patent No. GB-A-2 224703 assigned to Sumitomo Rubber Ind., Ltd. is regarded as the most relevant prior art and it teaches the features found in the preamble of claim 1; wherein the maximum section width of the tire is greater than the rim flange width and the tread width is less than the rim flange width.
The subject matter of the present invention teaches a novel tire profile that appears to be contrary to both of the above prior art patents and another departure from the conventional wisdom of those of ordinary skill in the art.
An object of the present invention is to provide a tire profile that minimized the rolling resistance of tire while minimizing the effect of the tread compound selection. In other words desensitizing the tires rolling resistance performance as a function of tread compounding.
Another object of the invention is to provide a lightweight tire.
Another object of the invention is to improve treadwear service mileage.
These and other objectives have been demonstrated by the tire as described here below.
A radial ply pneumatic tire is disclosed. The tire 30 has a maximum section width SW, a maximum section height SH, the ratio of SH/SW defining the tire aspect ratio, the aspect ratio being 85% or less. The tire has a nominal rim diameter ND, a nominal rim flange width W, and a tread having a tread width, TW.
The tire 30 has the maximum section width SW being located within a radial distance X from the nominal rim diameter ND, the distance X being less than a 50% of the maximum section height SH and wherein the maximum section width SW is greater than the rim flange width W and the tread width TW is less than the rim flange width W.
Preferably the distance X is about 40% of the maximum section height SH. The maximum section width SW is preferably at least 10% greater than the nominal rim flange width W and the tread width is preferably a least 10% less than de nominal rim flange width W.
The tire 30 his a carcass structure 36 having one or more radial ply, the ply or plies extended to and at least one ply is wrapped about or otherwise attached to a pair of annular bead cores 35. The radial plies are reinforced by parallel cords 20. The tire 30 when mounted on its design rim 40 and inflated has the cords 20 placed in tension. At a location between the radial location of the maximum section width SW and the nominal rim diameter ND a line L1, drawn through a point Y, the point Y intersecting the bead at the location of the nominal rim diameter ND, and tangent to the sidewall 21 is inclined radially and axially inwardly at an angle xcex8 relative to the rim flange, xcex8 being less than 40xc2x0 in each sidewall 21.
The tire 30 has its sidewall 21, at a radial location Z between the location of the maximum section width SW and the radially outmost section height location SH, inclined such that a line L2 drawn through Z and tangent to the sidewall 21 radially inwardly and axially outwardly is inclined at an angle xcex2, relative to a plane perpendicular to the tires aids, xcex8 being 90% of xcex2 or greater in each sidewall 21. Preferably xcex8 is about equal to xcex2, most preferably in the range of 90-120% of xcex2.
The locations Y and Z he on an axis A passing through the centroid C of the sidewall, the axis A being perpendicular to the tire axis of rotation. The centroid C of each sidewall is defined by the area within the sidewall 21 and between a line 70 drawn through a tread edge 30A or 30B and a tangent to the axially inner portion of the bead area 33 at location 12.
Definitions
xe2x80x9cAspect ratioxe2x80x9d of the tire means the ratio of its section height (SH) to its section width (SW) multiplied by 100% for expression as a percentage.
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d means lines or directions that are parallel to the axis of rotation of the tire.
xe2x80x9cBeadxe2x80x9d means that part of the tire comprising an annular tensile member wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes toe guards and chafers, to fit the design rim.
xe2x80x9cBelt structurexe2x80x9d or xe2x80x9cReinforcing Beltsxe2x80x9d means at least two annular layers or plies of parallel cords, woven or unwove, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17 degrees to 27 degrees with respect to the equatorial plane of the tire.
xe2x80x9cCarcassxe2x80x9d means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.
xe2x80x9cCordxe2x80x9d means one of the reinforcement strands of which the plies in the tire are comprised.
xe2x80x9cDesign rimxe2x80x9d means a rim having a specified configuration and width. For the purposes of this specification, the design rim and design rim widths are as specified by the industry standards in effect in the location in which the tire is made. For example, in the United States, the design rims are as specified by the Tire and Rim Association. In Europe, the rims are as specified in the European Tyre and Rim Technical Organizationxe2x80x94Standards Manual and the term design rim means the same is the standard measurement rims. In Japan, the standard organization is The Japan Automobile Tire Manufacturer""s Association.
xe2x80x9cDesign rim widthxe2x80x9d means the specified distance axially between rim flanges. For the purpose of this specification, the design rim width (D) is taken as (the minimum recommended rim width plus the maximum recommended rim width)/2 as specified by the appropriate industry standards.
xe2x80x9cEquatorial plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread.
xe2x80x9cInnerlinerxe2x80x9d means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid within the tire.
xe2x80x9cNormal inflation pressurexe2x80x9d refers to the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cNormal loadxe2x80x9d refers to the specific design, inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cPlyxe2x80x9d means a continuous layer of rubber-coated parallel cords,
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d means directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cRadial-ply tirexe2x80x9d means a belted or circumferentially-restricted pneumatic fix in which the ply cords, which extend from bead to bead are laid at cord angles between 65xc2x0 and 90xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cSection heightxe2x80x9d (SH) means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.
xe2x80x9cSection widthxe2x80x9d (SW) means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded excluding elevations of the sidewalls due to labeling, decoration or protective bands.
xe2x80x9cSharp diameterxe2x80x9d means the diameter as measured radially across the tire through the axis to the points defined by the intersection of a fine extending tangent the bead seat or first surface and a line extending tangent the bead flange or second surface.
xe2x80x9cShoulderxe2x80x9d means the upper portion of a sidewall just below the tread edge. Affects cornering.
xe2x80x9cSidewallxe2x80x9d means that portion of a the between the tread and the bead.
xe2x80x9cTread width,xe2x80x9d means the arc length of the tread surface in the axial direction, that is, in a plane passing through the axis of rotation of the tire.